warning C4996: 'fopen' vs 'fopen_s'

[webking]

Hi all,

since my lecturer told us to set the level of compilation to treat warnings as errors, i keep getting this warning:

warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead

i'm using Visual Studio 2008 Pro.

this is the code:
out is FILE*

if ((strcmp(argv,"-o"))==0){
o_exist=TRUE;
out=fopen(argv[i+1],"w");
if (out==NULL){
mtm_error(err_OpenFailed);
return 1;
}
i+=2;
continue;
}

Does anybody know what the problem is?
We didn't learn fopen_s and we've been told to use only what was taught in class...